TOUPPER(3) Linux Programmer's Manual TOUPPER(3)
NAME
 toupper, tolower, toupper_l, tolower_l - convert uppercase or lowercase
SYNOPSIS
 #include <ctype.h>
 int toupper(int c);
 int tolower(int c);
 int toupper_l(int c, locale_t locale);
 int tolower_l(int c, locale_t locale);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
 toupper_l(), tolower_l():
 Since glibc 2.10:
 _XOPEN_SOURCE >= 700
 Before glibc 2.10:
 _GNU_SOURCE
DESCRIPTION
 These functions convert lowercase letters to uppercase, and vice versa.
 If c is a lowercase letter, toupper() returns its uppercase equivalent,
 if an uppercase representation exists in the current locale. Other-
 wise, it returns c. The toupper_l() function performs the same task,
 but uses the locale referred to by the locale handle locale.
 If c is an uppercase letter, tolower() returns its lowercase equiva-
 lent, if a lowercase representation exists in the current locale. Oth-
 erwise, it returns c. The tolower_l() function performs the same task,
 but uses the locale referred to by the locale handle locale.
 If c is neither an unsigned char value nor EOF, the behavior of these
 functions is undefined.
 The behavior of toupper_l() and tolower_l() is undefined if locale is
 the special locale object LC_GLOBAL_LOCALE (see duplocale(3)) or is not
 a valid locale object handle.
RETURN VALUE
 The value returned is that of the converted letter, or c if the conver-
 sion was not possible.
ATTRIBUTES
 For an explanation of the terms used in this section, see at-
 tributes(7).
 +-------------------------+---------------+---------+
 |Interface | Attribute | Value |
 +-------------------------+---------------+---------+
 |toupper(), tolower(), | Thread safety | MT-Safe |
 |toupper_l(), tolower_l() | | |
 +-------------------------+---------------+---------+
CONFORMING TO
 toupper(), tolower(): C89, C99, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
 toupper_l(), tolower_l(): POSIX.1-2008.
NOTES
 The standards require that the argument c for these functions is either
 EOF or a value that is representable in the type unsigned char. If the
 argument c is of type char, it must be cast to unsigned char, as in the
 following example:
 char c;
 ...
 res = toupper((unsigned char) c);
 This is necessary because char may be the equivalent signed char, in
 which case a byte where the top bit is set would be sign extended when
 converting to int, yielding a value that is outside the range of un-
 signed char.
 The details of what constitutes an uppercase or lowercase letter depend
 on the locale. For example, the default "C" locale does not know about
 umlauts, so no conversion is done for them.
 In some non-English locales, there are lowercase letters with no corre-
 sponding uppercase equivalent; the German sharp s is one example.
SEE ALSO
 isalpha(3), newlocale(3), setlocale(3), towlower(3), towupper(3), use-
 locale(3), locale(7)
COLOPHON
 This page is part of release 5.10 of the Linux man-pages project. A
 description of the project, information about reporting bugs, and the
 latest version of this page, can be found at
 https://www.kernel.org/doc/man-pages/.
GNU 2017年09月15日 TOUPPER(3)